This invention relates generally to digital memory systems and more particularly to digital memory systems which are adapted to store radio frequency signals and to enable subsequent retransmission of such signals.
As is known in the art, it is frequently desired to store a received radio frequency signal and later retransmit such signal. In one such system the received radio frequency signal is periodically sampled at or above the Nyquist frequency, each sample is next converted into a corresponding digital word and each digital word is then stored in a digital memory. When it is desired to retransmit, the stored digital words are sequentially read from the memory in the sequence in which they were stored and such digital words are converted into corresponding voltages to produce a radio frequency signal which is amplified and retransmitted.
With such arrangement the degree to which the retransmitted radio frequency signal resembles the received radio frequency signal is related, inter alia, to the degree of quantization of the samples, i.e. the number of bits in each digital word. On the other hand, the cost, weight and size of the memory system increases as the degree of quantization increases. In particular, as the number of bits representing each sample is reduced the retransmitted radio frequency signal will, as a result of the quantization error, include, in addition to a radio frequency signal having the frequency of the received signal, unwanted harmonics or spurious signals which distort and cause undesirable responses in the received signal which may interfere with the intended communication.